1. Field of the Invention
The present invention relates to an electropthographic photoconductor to be used in a printer, a copying machine, a facsimile machine, and so on using the method of electrophotography. Especially, the present invention relates to an electrophotographic photoconductor having an excellent surface-charge retention by an improved photoconductive material for a photosensitive layer of the photoconductor.
2. Description of the Prior Art
In general, technical features required of electrophotographic photoconductors include abilities to hold surface charges in a dark place, to generate charges by receiving light, and to transport the charges by receiving light. The electrophotographic photoconductors can be grouped into two different types: one is a single layered type and the other is a so-called multiple layered type. The single layered type photoconductor has a single layer that combines the above abilities, while the multiple layered type one has function-separated laminated layers including a first layer responsible for generating charges and a second layer responsible for holding surface-charges in a dark place and for transporting charges at the time of receiving light.
Carlson process can be applied on an image formation based on the method of electrophotography using one of the above photoconductors. The Carlson process includes the steps of: uniformly charging the surface of the photoconductor in the absence of light by causing a corona discharge by airbreakdown; forming a latent image (a charge pattern on the photoconductor that mirrors the information to be transformed into the real image) of characters, figures, and the like of a source document; developing the latent image by adhering toner particles to the latent image by virtue of the electric field created by the charges on the photoconductor; transferring the developed toner particles on the photoconductor to paper by corona charging the back of the paper with a charge opposite to that of the toner particles and permanently fixing the image to the paper by melting the toner into the paper surface; and discharging and cleaning the photoconductor of any excess toner using coronas, lamps, brushes and/or scraper blades, recovering the photoconductor for reuse.
Heretofore, the following photoconductive materials have been used for the above electrophotographic photoconductors. The photoconductive materials include a compound prepared by dispersing an inorganic photoconductive material such as selenium, selenium alloy, zinc oxide, or cadmium sulfide into a resin binder and a compound prepared by dispersing an organic photoconductive material such as poly-N-vinyl carbazole, polyvinyl anthrancene, phthalocyanine compound, or bis-azo compound in a resin binder, or by the vacuum deposition instead of the dispersion.
The process of purifying the phthalocyanine compound as one of the above organic photoconductive materials has been studied in various ways in many references including A. W. Snow, et al., Macromorecules, 17 (8), 1614 (1984). These references describes 2, 4, 6-tris (2'-cyanophenyl)-1, 3, 5-triazine (hereinafter, it is abbreviated as triazine) which is a trimer as a polymerization product of o-phthalonitriles except a phthalocyanine compound (hereinafter, the product is abbreviated as a phthalonitrile polymer) in particular.
As described above, it is a known fact that the man skilled in the art uses the phthalocyanine compound as a photoconductive material of the electorophotographic photoconductor. In addition, the process for purificating the phthalocyanine compound has been also studied in various ways. In spite of those considerable works, by the way, some of the products of o-phthalocyanine polymerization may be defined as materials responsible for the electrophotographic properties of the electrophotoconductor. In this case, however, they have not been defined to a satisfactory degree under present circumstance. That is to say, the relationship between the materials associated with the process of preparing phthalocyanine compound and the electrophotographic properties, especially a surface-charge retention of photoconductor have not been defined well in spite of indicating the examples of various studies of phthalocyanine compound and various preparing processes for purifying the phthalocyanine compound.